In 1990, the AIDS-related knowledge, attitudes, and practices of fifth year (final year) students at four Managuan high schools were assessed. This was done by means of a self-administered questionnaire completed by 451 students (155 males, 296 females) whose mean age was 18 years. Eighty-six percent of the subjects knew AIDS was transmitted sexually, but the percentages aware of other transmission pathways and effective preventive measures were much lower. Use of condoms was cited as a preventive measure by 41% of the students, but by significantly more male respondents than female respondents (55% of the males versus 33% of the females, p = 0.0001). Sixty-four percent of all the survey subjects (90% of the males, 50% of the females) reported experiencing sexual intercourse. Sixty percent of the respondents were "very much" worried about AIDS, but only 23% considered themselves at risk of contracting the disease. Among the sexually active students, 29% of the respondents (38% of the males but only 7% of the females, p = 0.001) indicated a change in sexual behavior because of AIDS. Reported behavior change was strongly associated with concern about AIDS, but the association between reported behavior change and perception of personal risk was weak. Overall, the survey indicated that knowledge about transmission and prevention of AIDS among Managuan high school students was insufficient, especially among females, indicating a need for health education including interventions specifically targeted at female youth.